It is known to dielectrically load helical antennas for operation at UHF frequencies, particularly compact antennas for portable radio communication devices such as cellphones, satellite telephones, handheld positioning units and mobile positioning units. This invention is applicable in these and other fields such as WiFi, i.e., wireless local area network, devices, MIMO, i.e., multiple-input/multiple-output systems and other receiving and transmitting wireless systems
Typically, such an antenna comprises a cylindrical ceramic core having a relative dielectric constant of at least 5, the outer surface of the core bearing an antenna element structure in the form of helical conductive tracks. In the case of a so-called “backfire” antenna, an axial feeder is housed in a bore extending through the core between proximal and distal transverse outer surface portions of the core, conductors of the feeder being coupled to the helical tracks via conductive surface connection elements on the distal transverse surface portion of the core. Such antennas are disclosed in Published British Patent Applications Nos. GB2292638, GB2309592, GB2399948, GB2441566, GB2445478, International Application No. WO2006/136809 and U.S. Published Application No. US2008-0174512A1. These published documents disclose antennas having one, two, three or four pairs of helical antenna elements or groups of helical antenna elements. WO2006/136809, GB2441566, GB2445478 and US2008-0174512A1 each disclose an antenna with an impedance matching network including a printed circuit laminate board secured to the distal outer surface portion of the core, the network forming part of the coupling between the feeder and the helical elements. In each case, the feeder is a coaxial transmission line, the outer shield conductor of which has connection tabs extending parallel to the axis through vias in the laminate board, the inner conductor similarly extending through a respective via. The antenna is assembled by, firstly, inserting the distal end portions of the coaxial feeder into the vias in the laminate board to form a unitary feeder structure, inserting the feeder, with the laminate board attached, into the passage in the core from the distal end of the passage so that the feeder emerges at the proximal end of the passage and the laminate board abuts the distal outer surface portion of the core. Next, a solder-coated washer or ferrule is placed around the proximal end portion of the feeder to form an annular bridge between the outer conductor of the feeder and a conductive coating on the proximal outer surface portion of the core. This assembly is then passed through an oven whereupon solder paste previously applied at predetermined locations on the proximal and distal faces of the laminate board, as well as the solder on the above-mentioned washer or ferrule, melts to form connections (a) between the feeder and the matching network, (b) between the matching network and the surface connection elements on the distal outer surface portion of the core, and (c) between the feeder and the conductive layer on the proximal outer surface portion of the core. Assembly and securing of the feeder structure of the core is, therefore, a three-step process, i.e., insertion, placing of the washer or ferrule, and heating. It is an object of this invention to provide an antenna which is simpler to assemble.